Supersonic speed

From Conservapedia

Any speed that is faster than the speed of sound in the substance of interest.[1]

The prefix Mach is used to describe an airplane's true airspeed relative to the local speed of sound. It derives form Ernst Mach, a Czech born, German scientist who contributed to the study of sound. When a plane moves at the speed of sound (in air) it is Mach 1. When twice the speed of sound it is Mach 2. At Mach 0.5, an airplane is travelling at half the local speed of sound. When a plane passes the sound barrier (flying faster than sound travels) listeners hear a sonic boom.

The speed of sound in air is 770 mph, or 1130 ft/s (1230 km/h or 344m/s) in dry air at 70F [2]. Sound travels faster in water than it does in air, and even faster in iron and steel.